Trunking communication system has the main characteristic of channel sharing and dynamically using, it is a commanding and dispatching system, and in developed countries which have higher demand of trunking service, it is widely used in the field such as enterprise, facility, industry and mining, oil field, farm, public security, police agent, army and etc.
The main characteristic of the CDMA (Code Division Multiple Access) trunking communication system lies in: using half-duplex communication mode, fast call setup, and supporting group call (viz. a one-to-many calling mode). In the CDMA trunking communication system it requires group users to share forward channels in the same cell, the user can push the PTT(push-to-talk) key to talk to the other group members during group call. Such PTT service is widely used in walkie-talkie system and trunking system for serving commanding and dispatching function to fleet, such as public safety, fire protection, traffic and transport, airport and aviation, building site, massive congregation, military dispatch and etc. With the advancement of the society and quick development of the mobile communication technology, the field of personal communication becomes broader and broader, also trunking service turns to personal application gradually, e.g. group chat between young people, communication between members within a family and etc. Demand brings innovation, and application brings advancement of product, along with the wide development of mobile communication value-added service, the CDMA standard trunking communication system with group call and information transmission functions becomes a new mobile value-added service.
In trunking communication, each fleet has a certain active area, which is called the dispatch service area, in this specific service area, all fleet members can perform trunking communication. When a user is out of the dispatch service area, the system will not provide trunking service any more, here a out-the-dispatch-area indication will be displayed on the screen of a mobile station. So far there is no method for setting up dispatch service areas in a digital trunking system based on CDMA technology.